Problem: A block is on an inclined plane of 30 degrees with a block that is 8.5 kg. Find the tension of the cord and the normal force acting on the block. If the cord is cut, find the magnitude of the resulting acceleration of the block.

I know that tension = (mass)(acceleration), which i switched to (mass)(gravity). One of my friends said that you should multiply (mass)(gravity) by (sin30), but what about the problem says that it should be (sin30)....why shouldn't it be (cos30)?